ESAT Biology: Enzymes and animal physiology, set 1

• Answer all questions. No calculator.
• Each question has exactly one correct answer.

1. 11 mark

   A student is asked to summarise what enzymes are and how they work in general terms, before studying particular examples. Which statement most accurately describes enzymes?

   1. A Enzymes are lipids that lower the activation energy of a reaction and are broken down in the process.
   2. B Enzymes are proteins that act as biological catalysts, speeding up reactions without being used up themselves.
   3. C Enzymes are carbohydrate polymers that provide the energy needed to drive metabolic reactions forward.
   4. D Enzymes are proteins that are permanently changed by each reaction they catalyse, so a fresh molecule is needed for every reaction.
2. 21 mark

   An enzyme is described as being specific to one particular substrate. Which explanation of enzyme specificity is correct, in terms of the active site?

   1. A Specificity occurs because every enzyme has an identical active site shape, so a molecule that is merely the right size can bind and react, whichever enzyme it happens to meet.
   2. B Specificity occurs because the enzyme reshapes its own active site to match whichever substrate arrives, so a single enzyme can catalyse many different reactions equally well.
   3. C Specificity occurs because the active site is a fixed region that only checks substrate size, so any molecule of the correct size fits regardless of its chemical groups.
   4. D Specificity occurs because the active site has a shape complementary to one particular substrate, so only that particular substrate can normally bind to it and react.
3. 31 mark

   The rate of a particular enzyme-catalysed reaction was measured at four temperatures, with pH and substrate concentration both kept constant. Results: at 20 degrees C the relative rate was 20; at 30 degrees C it was 40; at 40 degrees C it was 78; at 50 degrees C it was 15. Based on these results, which statement is the best interpretation?

   1. A The rate roughly doubles at each step between 20 and 40 degrees C as temperature rises, then falls away sharply at 50 degrees C because the enzyme denatures.
   2. B The rate increases at every temperature tested, since a higher temperature always raises the kinetic energy of enzyme and substrate molecules.
   3. C The fall in rate at 50 degrees C shows substrate concentration became limiting at that temperature, a separate effect from the enzyme's own structure changing.
   4. D The results show the enzyme's optimum temperature is 50 degrees C, since it was the highest temperature tested and rate always peaks at the highest value tried.
4. 41 mark

   A sample of food is treated separately with three digestive enzymes: amylase, protease and lipase. Which row correctly matches each enzyme to the substance it breaks down and the products formed?

   1. A Amylase breaks down proteins into amino acids; protease breaks down starch into simple sugars; lipase breaks down fats into fatty acids and glycerol.
   2. B Amylase breaks down fats into fatty acids and glycerol; protease breaks down proteins into amino acids; lipase breaks down starch into simple sugars.
   3. C Amylase breaks down starch into simple sugars; protease breaks down proteins into amino acids; lipase breaks down fats into fatty acids and glycerol.
   4. D Amylase breaks down starch into amino acids; protease breaks down proteins into fatty acids and glycerol; lipase breaks down fats into simple sugars.
5. 51 mark

   During a sprint, a runner's muscle cells cannot get enough oxygen delivered fast enough to meet demand, so some cells respire anaerobically. Which pair of word equations correctly represents aerobic and anaerobic respiration in these muscle cells?

   1. A Aerobic: glucose -> lactic acid + carbon dioxide. Anaerobic: glucose + oxygen -> lactic acid + water.
   2. B Aerobic: glucose + oxygen -> carbon dioxide + water. Anaerobic: glucose -> lactic acid.
   3. C Aerobic: glucose -> carbon dioxide + water. Anaerobic: glucose + oxygen -> lactic acid + carbon dioxide.
   4. D Aerobic: glucose + oxygen -> ethanol + carbon dioxide. Anaerobic: glucose -> lactic acid + oxygen.
6. 61 mark

   A person accidentally touches a very hot object and withdraws their hand before feeling pain. Which sequence correctly places the components of the reflex arc in the order the nerve impulse travels?

   1. A Receptor -> sensory neurone -> relay neurone -> motor neurone -> effector.
   2. B Receptor -> motor neurone -> relay neurone -> sensory neurone -> effector.
   3. C Receptor -> relay neurone -> sensory neurone -> motor neurone -> effector.
   4. D Effector -> sensory neurone -> relay neurone -> motor neurone -> receptor.
7. 71 mark

   Two model alveoli are represented as cubes: cube P has a side length of 1 mm, and cube Q has a side length of 2 mm. Both are used to explain why smaller alveoli are more efficient at gas exchange, based on surface area to volume ratio. What is the surface area to volume ratio of cube P, and of cube Q?

   1. A Cube P has a surface area to volume ratio of 3, and cube Q has a ratio of 6, so the larger cube Q ends up with the higher surface area to volume ratio of the two cubes.
   2. B Cube P has a surface area to volume ratio of 1, and cube Q has a ratio of 2, obtained simply by taking the ratio of their side lengths as if it already were the answer.
   3. C Cube P has a surface area to volume ratio of 6, and cube Q has a ratio of 12, because doubling the side length is assumed to double both quantities by the same factor.
   4. D Cube P has a surface area to volume ratio of 6, and cube Q has a ratio of 3, so the smaller cube P ends up with exactly twice the ratio that the larger cube Q has.
8. 81 mark

   Which statement correctly compares the structure of arteries, veins and capillaries in terms of their function?

   1. A Arteries have thin walls and wide lumens to accommodate the high-pressure blood leaving the heart, capillaries have thick muscular walls to control the rate of local exchange, and veins have valves that hold back the very high pressure blood returning to the heart.
   2. B Arteries have walls one cell thick to allow rapid exchange with tissues, capillaries are thick and muscular to resist the pressure of blood passing through them, and veins have valves because venous blood is at higher pressure than arterial blood.
   3. C Arteries have thick, muscular, elastic walls to withstand high-pressure blood leaving the heart, capillaries have walls one cell thick to allow efficient exchange, and veins have valves to prevent backflow of the lower-pressure blood they carry back to the heart.
   4. D Capillaries have thick muscular walls to control local blood pressure, arteries have walls one cell thick to allow gas and nutrient exchange directly with tissues, and veins have no valves because their blood pressure is already too low to flow backwards.
9. 91 mark

   A student lists the components of blood and one function for each: red blood cells, white blood cells, platelets and plasma. Which row correctly matches each component to its main function?

   1. A Red blood cells carry oxygen around the body; white blood cells make antibodies and carry out phagocytosis; platelets are responsible for clotting blood; plasma transports dissolved substances such as hormones and carbon dioxide.
   2. B Red blood cells are responsible for blood clotting at a wound; white blood cells are the ones that carry oxygen around the body; platelets are the cells that produce antibodies; plasma's only role is phagocytosis.
   3. C Red blood cells carry oxygen around the body; white blood cells are involved in blood clotting rather than immunity; platelets produce antibodies and carry out phagocytosis; plasma transports only water and nothing else.
   4. D Red blood cells are responsible for transporting hormones and antibodies around the body; white blood cells are the ones that carry oxygen; platelets transport carbon dioxide; plasma is involved in phagocytosis rather than transport.
10. 101 mark

    A student lists four processes that occur as food passes through the digestive system: peristalsis, digestion, absorption and egestion. Which set of definitions correctly matches each term?

    1. A Peristalsis is the chemical breakdown of large food molecules into smaller, soluble ones; digestion is the wave-like muscular contraction that moves food along the gut; absorption is the movement of digested food molecules into the blood; egestion is the removal of undigested food (faeces) from the body.
    2. B Peristalsis is the wave-like muscular contraction that moves food along the gut; digestion is the breakdown of large food molecules into smaller, soluble ones; absorption is the movement of digested food molecules into the blood; egestion is the removal of undigested food (faeces) from the body.
    3. C Peristalsis is the wave-like muscular contraction that moves food along the gut; digestion is the breakdown of large food molecules into smaller, soluble ones; absorption is the removal of undigested food (faeces) from the body; egestion is the movement of digested food molecules into the blood.
    4. D Peristalsis is the wave-like muscular contraction that moves food along the gut; digestion is the movement of digested food molecules into the blood; absorption is the chemical breakdown of large food molecules into smaller, soluble ones; egestion is the removal of undigested food (faeces) from the body.
11. 111 mark

    Which statement correctly describes the role of the kidney and the nephron in the human excretory system?

    1. A The kidney's main role is to store urine until it is released from the body, while each nephron's role is to produce hormones that directly regulate heart rate and blood pressure.
    2. B Each nephron filters the blood only once every 24 hours, removing all of the day's urea in a single batch that is then stored, unmodified, as urine inside the kidney.
    3. C The nephron's only function is to reabsorb all of the water and glucose reaching it from the blood, so that neither substance can ever appear in urine, whatever the body's hydration or energy needs happen to be.
    4. D The kidney contains many nephrons, each filtering the blood and then selectively reabsorbing useful substances, leaving waste such as urea and excess water to be excreted as urine, which contributes to homeostasis.
12. 121 mark

    After a carbohydrate-rich meal, a person's blood glucose concentration rises above its normal range. Which sequence correctly describes how the body responds, in terms of negative feedback?

    1. A The pancreas detects the rise in blood glucose and releases glucagon, which causes the liver to convert its stored glycogen back into glucose, raising blood glucose even further above normal.
    2. B The pancreas detects the rise and releases insulin, which causes body cells throughout the body to convert glucose into glycogen for storage, which then raises blood glucose even further above normal.
    3. C The pancreas detects the rise and releases insulin, which causes liver and muscle cells to take up glucose and store it as glycogen, lowering blood glucose back down towards its normal range.
    4. D The pancreas detects the rise and releases insulin, which then causes the liver to convert its stored glycogen back into free glucose, lowering blood glucose back down towards its normal range.
13. 131 mark

    In the menstrual cycle, four named hormones interact to control ovulation and the build-up of the uterus lining. Which statement correctly describes one of their roles?

    1. A FSH (follicle-stimulating hormone) is released from the pituitary gland, stimulates an egg to mature in the ovary, and also stimulates the ovary to produce oestrogen as the cycle progresses.
    2. B Oestrogen is released directly from the pituitary gland, and it is oestrogen itself that directly triggers ovulation, the release of an egg, without any other hormone being involved at all.
    3. C LH (luteinising hormone) is released at a constant, low level throughout the whole cycle, with no surge at any point, and it plays no part whatsoever in triggering ovulation.
    4. D Progesterone is released from the ovary in the days before ovulation, and its main role there is to stimulate the pituitary gland into releasing FSH so that a new egg begins maturing.
14. 141 mark

    A vaccine containing a dead or inactive form of a pathogen is given to a healthy person. Which explanation correctly describes how this protects the person against future infection by the live pathogen?

    1. A The dead or inactive pathogen material directly kills any live pathogen the person meets later on, acting like a stored chemical weapon that works without the immune system being involved at all.
    2. B The dead or inactive pathogen carries antigens that stimulate white blood cells to produce antibodies and memory cells; meeting the live pathogen later triggers a faster, stronger response from those memory cells.
    3. C The dead or inactive pathogen provides a dose of antibiotics that stays in the bloodstream permanently and goes on to destroy the live pathogen whenever it is encountered again in future.
    4. D The dead or inactive pathogen causes the body to become permanently immune by making sure the pathogen's antigens can never be recognised by the immune system again, on any future exposure.
15. 151 mark

    A patient with coronary heart disease is being considered for different treatments. Which statement correctly matches a named treatment to its category and general action?

    1. A Statins are actually a surgical procedure, not a medicine at all, that physically widens a narrowed coronary artery from the inside using a small inflatable balloon and a mesh tube called a stent.
    2. B A coronary bypass is in fact a type of medication, taken as a daily tablet, that gradually lowers blood cholesterol levels over a period of several months rather than being any kind of operation.
    3. C Anti-hypertensive drugs are actually surgical procedures in which a healthy blood vessel is grafted around a section of coronary artery that has become blocked, rather than being any form of tablet.
    4. D Statins are a lifelong medication that lowers blood cholesterol levels, while a coronary bypass is the surgical procedure that grafts a healthy blood vessel around a blocked section of coronary artery.

Worked solutions

Every question below carries the reasoning, not just the answer. The official material for this test publishes a correct option letter and nothing else.

1. Question 1Answer: B

   1. An enzyme's identity is set by its molecular class: enzymes are proteins, built from folded chains of amino acids, not carbohydrates or lipids.
   2. A biological catalyst speeds up the rate of a reaction by providing an alternative pathway with a lower activation energy.
   3. A defining property of any catalyst, biological or otherwise, is that it is not used up or permanently changed by the reaction it catalyses, so the same enzyme molecule can be reused many times.
   4. Only option B combines both facts correctly: protein structure, and catalytic (not consumed) behaviour, so B is correct.
   • Why not A: Confuses enzymes with lipids, and wrongly assumes a catalyst is consumed by the reaction it speeds up.
   • Why not C: Confuses enzymes with carbohydrates and wrongly treats an enzyme as an energy source rather than a catalyst.
   • Why not D: Treats the enzyme as a reactant rather than a catalyst; a catalyst is chemically unchanged at the end of the reaction, so it can be reused.

2. Question 2Answer: D

   1. Each enzyme has a specific three-dimensional shape, and part of that shape forms the active site, the region where the substrate binds.
   2. The active site's shape is complementary to the shape (and chemical groups) of one substrate, or a small group of very similar substrates, which is why an enzyme is described as specific.
   3. Because specificity depends on the shape of the active site being complementary to a particular substrate, changing that shape (for example by denaturation) removes the enzyme's activity even though its chemical composition is otherwise unchanged.
   4. Only D captures the complementary-shape basis of specificity correctly, so D is the answer.
   • Why not A: Wrongly claims every active site has the same shape and that size alone determines binding; active site shapes (and their chemical groups) differ between enzymes.
   • Why not B: Overstates the flexibility of the active site; some flexing (induced fit) occurs around a matching substrate, but the site does not reshape itself to fit any arbitrary substrate.
   • Why not C: Reduces specificity to substrate size alone, ignoring that the chemical groups and precise geometry of the active site must also match the substrate.

3. Question 3Answer: A

   1. Reading the data, rate rises from 20 at 20 degrees C to 40 at 30 degrees C to 78 at 40 degrees C, roughly doubling with each 10 degree rise, consistent with increased kinetic energy causing more frequent, effective collisions between enzyme and substrate.
   2. At 50 degrees C the rate drops sharply to 15, well below the value at 40 degrees C, even though substrate concentration and pH were both held constant.
   3. The only factor that changed between 40 and 50 degrees C is temperature, and above an enzyme's optimum temperature its tertiary structure begins to break down (denaturation), distorting the active site so fewer successful enzyme-substrate collisions occur.
   4. So the pattern shown is rate rising towards an optimum near 40 degrees C, then falling sharply as the enzyme denatures at 50 degrees C, exactly what option A describes.
   • Why not B: Ignores that above the optimum temperature the enzyme denatures, so rate does not keep rising with temperature; the data show a fall at 50 degrees C, contradicting this claim.
   • Why not C: Misattributes the fall in rate to substrate availability rather than to the enzyme's own structure changing (denaturation), when the question states substrate concentration was kept constant.
   • Why not D: Confuses the highest temperature tested with the optimum temperature, and wrongly assumes rate always peaks at whichever value was tried last; the data show the rate is actually highest at 40 degrees C.

4. Question 4Answer: C

   1. Amylase is a carbohydrase: it hydrolyses starch (a polysaccharide) into simple sugars such as maltose and glucose.
   2. Protease hydrolyses proteins by breaking the peptide bonds between amino acids, releasing individual amino acids.
   3. Lipase hydrolyses fats (lipids) into their component fatty acids and glycerol.
   4. Matching each enzyme to its correct substrate and correct products gives amylase-starch-sugars, protease-protein-amino acids, and lipase-fat-fatty acids/glycerol, exactly option C.
   • Why not A: Swaps the roles of amylase and protease: amylase acts on starch (a carbohydrate), not on protein, and protease acts on protein, not starch.
   • Why not B: Swaps the roles of amylase and lipase: amylase acts on starch, not fat, and lipase acts on fat, not starch.
   • Why not D: Keeps the correct enzyme-substrate pairs but jumbles the products between rows, giving each substrate the wrong breakdown product.

5. Question 5Answer: B

   1. Aerobic respiration in animal cells requires oxygen as a reactant and fully oxidises glucose, releasing carbon dioxide and water as waste products: glucose + oxygen -> carbon dioxide + water.
   2. When oxygen cannot be supplied fast enough, as in intense exercise, animal muscle cells switch to anaerobic respiration, which does not use oxygen and only partially breaks down glucose.
   3. In animal cells the anaerobic pathway produces lactic acid, not carbon dioxide, water, ethanol or oxygen: glucose -> lactic acid.
   4. Only option B pairs the correct reactants and products with each pathway, so B is correct.
   • Why not A: Puts oxygen into the anaerobic equation and lactic acid into the aerobic one; anaerobic respiration in animal cells happens precisely because oxygen is not available, so it cannot appear as a reactant there, and lactic acid (not carbon dioxide and water) is the anaerobic product.
   • Why not C: Leaves oxygen out of aerobic respiration, when oxygen is required as a reactant for aerobic respiration to occur, and wrongly adds it to the anaerobic equation instead.
   • Why not D: Uses ethanol as the anaerobic product, which is the pathway in yeast and plant cells, not the lactic acid pathway used by animal muscle cells, and wrongly shows oxygen as a product of anaerobic respiration.

6. Question 6Answer: A

   1. A receptor (here, a pain/heat receptor in the skin) detects the stimulus and generates a nerve impulse.
   2. A sensory neurone carries that impulse from the receptor towards the central nervous system (brain and spinal cord).
   3. Inside the spinal cord, a relay neurone connects the sensory neurone to a motor neurone, allowing a fast response without waiting for the brain to process the sensation.
   4. The motor neurone carries the impulse out to an effector (a muscle), which contracts to withdraw the hand, giving the order receptor, sensory neurone, relay neurone, motor neurone, effector, as in option A.
   • Why not B: Reverses the sensory and motor neurones; the sensory neurone must carry the impulse into the central nervous system before the motor neurone can carry a response out to the effector.
   • Why not C: Places the relay neurone before the sensory neurone; the relay neurone sits inside the central nervous system and can only pass on an impulse it has already received from a sensory neurone.
   • Why not D: Swaps the receptor and the effector, which reverses the whole pathway; the receptor detects the stimulus at the start of the arc, and the effector (here, a muscle) produces the response at the end.

7. Question 7Answer: D

   1. For a cube, surface area = 6 x side^2 and volume = side^3, so the surface area to volume ratio is 6 x side^2 / side^3 = 6/side.
   2. Cube P has side 1 mm, so its surface area to volume ratio is 6/1 = 6.
   3. Cube Q has side 2 mm, so its surface area to volume ratio is 6/2 = 3.
   4. Cube P (the smaller cube) has a ratio of 6 against cube Q's ratio of 3, twice as high, which is exactly why smaller alveoli, and other small exchange structures, are more efficient at gas exchange per unit volume, matching option D.
   • Why not A: Gets the two ratios the right size but assigns them to the wrong cube, wrongly concluding the larger cube has the higher surface area to volume ratio, when a smaller object always has a higher ratio for the same shape.
   • Why not B: Uses the ratio of the side lengths (1:2) directly as if it were the surface area to volume ratio, instead of separately calculating surface area (6 x side^2) and volume (side^3) for each cube.
   • Why not C: Wrongly assumes that doubling the side length doubles the surface area to volume ratio by the same factor; in fact surface area scales with the square of the side length and volume scales with the cube, so the ratio (surface area / volume) actually halves when the side length doubles.

8. Question 8Answer: C

   1. Arteries carry blood away from the heart at high pressure, so they have thick walls containing muscle and elastic fibres, which withstand and help maintain that pressure.
   2. Capillaries are the site of exchange between blood and tissues, so their walls are only one cell thick, minimising the diffusion distance for gases, glucose and other substances.
   3. Veins carry blood back to the heart at much lower pressure than arteries, so their walls are thinner, and they contain valves at intervals to stop blood flowing backwards under gravity or low pressure.
   4. Option C correctly assigns thick elastic walls to arteries, one-cell-thick walls to capillaries, and valves to the lower-pressure veins, so C is correct.
   • Why not A: Swaps the wall descriptions for arteries and veins, and wrongly gives capillaries thick muscular walls; arteries need thick, elastic, muscular walls to withstand high pressure, veins have valves because their blood is at LOW pressure, and capillary walls are one cell thick, not muscular.
   • Why not B: Swaps arteries and capillaries, and gives the correct anatomical fact about vein valves but the wrong reason; capillary walls (not artery walls) are one cell thick for exchange, and venous blood is at LOWER pressure than arterial blood, which is exactly why the valves are needed.
   • Why not D: Swaps the descriptions of capillaries and arteries, and wrongly claims veins have no valves; veins do have valves precisely because their low-pressure blood would otherwise flow backwards under gravity.

9. Question 9Answer: A

   1. Red blood cells contain haemoglobin and are specialised to carry oxygen around the body.
   2. White blood cells are part of the immune system: some produce antibodies, and others carry out phagocytosis, engulfing pathogens.
   3. Platelets are cell fragments involved in blood clotting at a wound, sealing the site and preventing blood loss and infection.
   4. Plasma is the liquid part of blood, and it transports dissolved substances such as hormones, antibodies, urea and carbon dioxide, as well as distributing heat around the body, so option A is the only row that assigns each function to its correct component.
   • Why not B: Randomly reassigns every function: clotting is the role of platelets, not red blood cells; oxygen transport is the role of red blood cells, not white blood cells; antibody production is a white blood cell function, not a platelet one; and transport of dissolved substances is plasma's role, not phagocytosis.
   • Why not C: Swaps the roles of white blood cells and platelets (clotting is a platelet function, and antibody production/phagocytosis are white blood cell functions), and understates plasma, which transports far more than water, including hormones, antibodies, urea and carbon dioxide.
   • Why not D: Gives red blood cells a transport role that belongs to plasma, gives white blood cells the oxygen-carrying role that belongs to red blood cells, and gives platelets a transport role instead of their actual clotting function.

10. Question 10Answer: B

    1. Peristalsis is a mechanical process: coordinated waves of muscular contraction along the gut wall that physically push food along.
    2. Digestion is a chemical process: enzymes break down large, insoluble food molecules (starch, protein, fat) into smaller, soluble molecules that can be absorbed.
    3. Absorption is the movement of these small, soluble digested molecules across the gut wall into the blood, mainly in the small intestine.
    4. Egestion is the passing out of undigested material (faeces) from the body, through the large intestine and anus, a different process from excretion of metabolic waste, and only option B assigns all four terms correctly.
    • Why not A: Swaps peristalsis and digestion: peristalsis is a mechanical, muscular process that moves food along the gut, while digestion is the chemical breakdown of food into smaller molecules; absorption and egestion here are correctly defined.
    • Why not C: Swaps absorption and egestion: absorption is digested food entering the blood (typically in the small intestine), while egestion is the removal of undigested material (faeces) from the body; peristalsis and digestion here are correctly defined.
    • Why not D: Swaps digestion and absorption: digestion is the chemical breakdown of food, while absorption is the subsequent movement of the digested products into the blood; peristalsis and egestion here are correctly defined.

11. Question 11Answer: D

    1. The kidney is the organ of excretion for water-soluble waste, and each kidney contains roughly a million tiny filtering units called nephrons.
    2. Each nephron filters the blood under pressure, removing small molecules (including urea, salts, glucose and water) from the blood into the nephron tubule.
    3. As the filtrate flows along the nephron, useful substances (all of the glucose, and a regulated amount of water and salts, depending on the body's needs) are selectively reabsorbed back into the blood.
    4. What remains, mainly urea, excess salts and excess water, passes on as urine, so the kidney and its nephrons together remove metabolic waste and help keep the internal environment (homeostasis) stable, exactly what option D describes.
    • Why not A: Confuses the kidney with the bladder, the organ that actually stores urine, and invents a hormone-producing role for the nephron that has nothing to do with the real function of filtration and reabsorption.
    • Why not B: Invents a once-a-day batch mechanism; nephrons continuously filter blood as it flows through the kidneys, moment to moment, rather than processing it in one daily batch.
    • Why not C: Overstates reabsorption as complete and fixed; the nephron reabsorbs useful substances according to the body's needs (for example, reabsorbing more or less water depending on hydration), and healthy urine still contains water rather than none.

12. Question 12Answer: C

    1. Blood glucose concentration is monitored and controlled by negative feedback, which acts to return a variable that has moved away from its normal range back towards it.
    2. When blood glucose rises above the normal range, the pancreas detects this and secretes insulin into the blood.
    3. Insulin causes liver and muscle cells to take up glucose from the blood and convert it into glycogen for storage, which removes glucose from the bloodstream.
    4. This lowers blood glucose concentration back towards its normal range, completing the negative feedback loop, exactly what option C describes; glucagon has the opposite role, released when blood glucose is too low, causing the liver to convert stored glycogen back into glucose.
    • Why not A: Releases glucagon, the hormone that responds to LOW blood glucose by raising it, when the situation described is a rise in blood glucose that needs to be lowered; it also has the direction of glycogen conversion the wrong way round for raising glucose.
    • Why not B: Correctly identifies insulin and correctly describes glucose being converted to glycogen, but then wrongly concludes this raises blood glucose further; converting glucose into glycogen for storage removes glucose from the blood, so it lowers, not raises, blood glucose, which is what negative feedback requires here.
    • Why not D: Names the correct hormone (insulin) but describes the wrong conversion direction; converting glycogen into glucose would raise blood glucose further, the opposite of the corrective response insulin actually triggers when glucose is already too high.

13. Question 13Answer: A

    1. FSH (follicle-stimulating hormone) is released from the pituitary gland and causes an egg to begin maturing inside a follicle in the ovary.
    2. FSH also stimulates the ovary to produce oestrogen, which itself causes the lining of the uterus to build up and, at a high enough level, triggers the pituitary gland to release a surge of LH.
    3. This LH surge is what triggers ovulation, the release of the mature egg from the ovary.
    4. After ovulation, the remaining follicle develops into the corpus luteum, which releases progesterone to maintain the uterus lining and inhibit further FSH and LH release, so option A is the only statement here that correctly places FSH's origin and both of its effects.
    • Why not B: Wrongly places oestrogen's origin in the pituitary gland (it is released by the ovary) and wrongly has oestrogen triggering ovulation directly; ovulation is actually triggered by a surge in LH.
    • Why not C: Understates LH almost entirely: LH is released at a low level for most of the cycle but then surges sharply partway through, and that LH surge is what triggers ovulation.
    • Why not D: Reverses progesterone's timing and role: progesterone is released mainly after ovulation, from the corpus luteum, and it maintains the uterus lining while inhibiting further FSH and LH release, not stimulating FSH.

14. Question 14Answer: B

    1. A vaccine introduces antigens, carried on a dead or inactivated form of the pathogen, into the body without causing the disease itself.
    2. These antigens are recognised by the immune system, which responds by producing antibodies specific to those antigens, and also produces memory cells that persist long after the initial exposure.
    3. If the person is later exposed to the live pathogen carrying the same antigens, the memory cells allow a much faster and stronger secondary antibody response than would occur without prior exposure.
    4. This rapid response usually clears the pathogen before it can multiply enough to cause symptoms, so the person is protected, the mechanism option B describes correctly.
    • Why not A: Removes the immune system from the explanation entirely; a vaccine works by provoking the person's own immune response, not by vaccine material itself acting as a stored poison against a future pathogen.
    • Why not C: Confuses vaccination with antibiotic treatment; a vaccine does not contain or release antibiotics, and antibiotics do not treat viral infections at all, unlike the antibody-based protection a vaccine provides.
    • Why not D: Reverses the mechanism; memory cells produced after vaccination make antigens MORE quickly recognised on a later exposure, not permanently un-recognisable, and that faster recognition is exactly what gives protection.

15. Question 15Answer: D

    1. Cardiovascular disease can be treated or managed with lifelong medication, including statins, which lower blood cholesterol levels and so reduce the build-up of fatty deposits in artery walls.
    2. Other medications used include anti-coagulants, which reduce the tendency of blood to clot, and anti-hypertensive drugs, which lower blood pressure.
    3. Surgical procedures are used for more severe narrowing or blockage: a stent holds a narrowed artery open, and a coronary bypass grafts a healthy blood vessel around a blocked section of artery to restore blood flow.
    4. Only option D correctly keeps statins as a medication (lowering cholesterol) and a coronary bypass as a surgical graft procedure, matching each named treatment to its correct category and action.
    • Why not A: Describes a stent/angioplasty style surgical procedure accurately but wrongly names it a statin; a statin is a cholesterol-lowering medication, not any kind of surgical or catheter-based procedure.
    • Why not B: Describes what a statin actually does (lowers blood cholesterol as a daily tablet) but wrongly labels this a coronary bypass, which is a surgical operation, not a medication.
    • Why not C: Describes a coronary bypass operation accurately but wrongly labels it an anti-hypertensive drug; anti-hypertensive drugs are medications that lower blood pressure, not a surgical grafting procedure.